The most abundant tissue in the human body is soft tissue, and most soft tissue is collagen. Indeed, over 90% of the organic matter in tendons and ligaments is collagen. The connective tissue in joints is comprised of soft tissue, generally collagen tissue. When soft tissue in a joint is damaged, the healing process is often long and painful.
Well-known methods for addressing the treatment of soft tissue in injured joints include strengthening exercises, open surgery, and arthroscopic techniques. Using current treatments, many people with injured joints suffer from prolonged pain, loss of motion, nerve injury, and some develop osteoarthritis. The soft tissue in many injured joints never heals enough to return the damaged joint to its full range of function.
It is known in the art to apply thermal energy to soft tissue, such as collagen tissue, in joints to try to alter or manipulate the tissue to provide a therapeutic response during thermal therapy. In particular, applying controlled thermal energy to soft tissue in an injured joint can cause the collagenous tissue to shrink, thereby tightening unstable joints.
Medical probes for the rehabilitative thermal treatment of soft tissues are known in the art. Examples of these probes include laser probes and RF heated probes. While these probes meet the basic need for rehabilitative thermal treatment of soft tissues, such as collagen tissues, many suffer from temperature overshoot and undershoot fluctuation, causing unpredictable results in the thermal alteration.
Many existing temperature control methodologies rely upon algorithms that are continuous, for example, algorithms such as disclosed in the above-referenced U.S. Pat. No. 6,162,217 (1999) for a “Method and Apparatus for Controlling a Temperature-Controller Probe”. Continuous algorithm-based methods can control temperature well in systems are that themselves continuous, i.e., systems in which there is no abrupt change in media temperature, media consistency, head load, cooling effects, etc.
Other approaches seem to be less successful in their attempts to delivery uniform energy from a probe in a thermally unstable environment. For example U.S. Pat. No. 5,458,596 to Lax, et al., discloses examples of a probe with a proximal and distal end that employs heat for the controlled contraction of soft tissue. But not unlike other prior art probes, probe temperature can become unstable as heat from the probe is dissipated into the mass of the treated tissue. This can be especially troublesome when treating dense tissue, which acts as a heat sink and thereby requires additional energy input to maintain a desired target temperature. The application of additional energy in an attempt to compensate for the heat sink effect can cause an under-damped effect before settling out at the desired temperature.
In general, a system is over-damped when its damping factor is greater than one, and the system will have a slow response time. A system is critically damped when its damping factor is exactly one. A system is under-damped when its damping factor is less than one. In an under-damped system, “ringing” is a problem and can result in the momentary application of temperatures that are too high for the safe heating of soft tissue. When this occurs, damage to the soft tissue may result from charring, ablation or the introduction of unwanted and harmful effects on the soft tissue causing injury.
Typically, medical probes are attached to a controller that controls the probe power output based on an actual temperature measurement from a temperature sensor such as a thermocouple in the probe, and a set predetermined target temperature. The controller is part of a system that includes circuitry to monitor temperature sensed by the temperature sensor. Temperature-controlled probes are designed to provide precise coagulation, to eliminate damage, charring, and bubbles. Different size probes with various configurations are available to treat various joint sizes including the shoulder, knee, ankle, wrist and the elbow.
Precise temperature control of the system in which the probes are used is required during various types of thermal therapy of soft tissue. For example, during hyperthermia, which is defined as the treatment of diseased soft tissue by raising the bodily temperature by physical means, some prior art probes have difficulty in providing smooth and consistent heating because the preferred materials for the energy delivery electrodes are highly thermally responsive materials. Such materials generally do not retain large amounts of heat energy. At initiation, the controller rapidly heats the probe to achieve the target temperature, which can result in an overshoot problem. During application, probe contact with large tissue masses tends to cause underdamped fluctuations in the probe temperature due to vast differences in the temperature of the surrounding tissue mass. Likewise, one skilled in the art will appreciate that similar problems may occur during a desired reduction in the soft tissue temperature.
In addition, different probes have different operating characteristics. Applications using larger probes typically need relatively large amounts of power to reach and maintain the desired temperature. Applications using smaller probes, such as a spine probe, need a well-controlled and precise stable temperature. However, the typical prior art controller uses the same method to control the power output for different probes and does not change the control process in response to different types of probes, further contributing to overshoot and undershoot problems.
Therefore, a method and apparatus are needed that allows the controller to change operation in response to the type of probe attached, preferably while reducing if not eliminating temperature overshoot and oscillation during treatment of tissue with the probe. More preferably, such method and apparatus should more rapidly produce adequate thermal energy at the tissue under treatment without overshooting or otherwise exceeding a desired target temperature, and without prematurely reducing thermal output power. In addition, such probe should be continuously controllable even in a thermally discontinuous environment such as arthroscopic environments.